The cerebellum plays a pivotal role in visuomotor behavior. Patients with cerebellar pathology demonstrate abnormal movement direction, velocity, and acceleration, poor eye-arm coordination, and an increased dependence on visual feedback during movement. However, the association between various kinematic parameters of movement and the discharge of cerebellar Purkinje cells remains poorly understood. Equally poorly defined is the contribution of visual information to the activity of these cells. The long-term objective of the proposed project attempts to define the representation of these visuomotor parameters in the discharge of Purkinje cells. Three specific aims guide this project: (1) Determine the relationship between Purkinje cell discharge and movement position, velocity, and acceleration; (2) Determine the extent to which premovement visual information about velocity and direction influences Purkinje cell discharge during movement; and (3) Determine the contribution of visual information to Purkinje cell discharge by evaluating movements performed with and without visual feedback. A series of two-dimensional, visually guided tracking tasks will be used to address these aims.